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At the Chalkboard: Failure Mechanism by Greg Glassman - CrossFit Journal

In ExPhysiology, Reference, Rest Day/Theory, Videos

February 05, 2010

Video Article

In front of a chalkboard for a discussion on exercise theory, Coach Greg Glassman suggests it’s possible certain muscles of the body can lift loads that can do damage to other parts of the body by compromising midline stability. To save us from ourselves, the body might short-circuit and fail before those loads severely injure an athlete.

For example, many people can lift one leg in an L-sit, but both legs fall to the floor when they attempt to raise the second limb. This phenomenon isn’t seen when one holds dumbbells away from the body at shoulder height. Most people can raise one arm and then the second without failing.

Coach Glassman has his own explanation for the phenomenon: “I suspect that there’s a built-in failure mechanism neurologically for this peripheral muscle tissue to prevent a midline collapse.”

In other words, the body may well be wired to prevent us from lifting loads that compromise midline stability and put us at risk of injury.

4min 06sec

Additional reading: Three Important Ab Exercises by Greg Glassman, published May 1, 2003.

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9 Comments on “At the Chalkboard: Failure Mechanism”


wrote …

In rough terms, muscles have neurological innervation for two purposes: One, to contract muscle tissue and elicit motion (alpha-motor neurons); Two, to sense the amount of stretch in a muscle (muscle spindles/gamma-motor neurons). Muscles spindles work together with golgi tendon organ (sensors that detect amounts of tension in a contracted muscles tendon) to prevent tissue damage from over-stretching or over-contracting. They do this by a feedback loop or reciprocal inhibition : too much stretch - loop a message to the same muscle - contract to decrease stretch / too much tension - send a message to the antagonist - contract to release agonist tension.

Many training injuries do not come as the result of direct trauma. They are the result of repetitive and poor mechanics, with the last action before tissue failure being the "straw that broke the camels back".

Long story short, Glassman is correct that the body protects itself. Even more important, great functional mechanics learned through crossfit or doctors/physicians/trainers who have a clue will provide for better neuro-musculo-skeletal synchronization and increase force production with less chance of injury.


wrote …

There's a receptor in the tendon called, in Spanish (I've not been able to find it in English, sorry) "Corp├║sculo Tendinoso de Golgi", not to be confused with the Golgi Body which is something totally different. Well, this receptor in the tendon shuts down muscle function when the muscle is taking on too much strain. This is the short version of the receptor's function. It could very well be that these receptors play a role in the failure mentioned in raising both legs. It's just a supposition but I would not totally discard it.


wrote …

I have this exact problem that Coach is talking about. I'm a newbie to CrossFit and that might be my problem right there. But whenever I do try to perform a L-sit my leg collapses just as Coach Glassman describes it. It really sucks that my core is that weak.


wrote …

Hey, a new definition for balance. I went to the dip bars and did an L-sit to help visualize. The analogy he used with leaning back while holding the dumbbells is the one I was going to use before watching the video. Then I watched the L-sit demo and confirmed it because the guy falls forward. It is the opposite of counterbalancing reflex. I am pretty sure it has a name, but I don't know or care what it is. Instead of the torso leaned forward, hips at an acute angle in relation to the chest and quads, and arms forming a triangle with the chest and legs about mid thigh to counterbalance the weight of the legs it causes the legs to drop to maintain a balanced posture. Ever watch a beginner squat with weight, sometimes they stand up before getting all the way down because they are falling off balance. Usually you see it when the squatter is losing balance to the rear. The brain sends a message to the hips and legs saying stand up stupid you are about to fall on your ass. Same thing here except the brain sends a message to the hip flexors to relax because the weight of both legs is pulling the body forward off balance. I am not a gymnast, but wouldn't this be a weakness in the shoulder girdle.


wrote …

He calls it a hypothesis, and right now it only is to him, and me, but I believe he is exactly correct. It seems that the exact same things happens when we flinch (ask Tony Bauer about that one), tense certain muscles when we get tackled, or our foot muscles flex every step when we run. These things have been hardwired into our genomes and nervous systems long, long before we were even human beings as we know it. My dogs do the same kind of things.

What's interesting to me is that (and I don't have actual statistics to back this up, just anecdotal experiences of others) whenever a guy hurts himself, it's very sudden. He reached down to catch something and his back tensed too hard in just a fraction of a second, and he pulled it. Or someone flips a mattress, and when they do the fast part of the lift (similar to the second pull on a clean), and they aren't nearly strong enough to do it, they hurt something.

My question is, if I'm right- does the body fail to react in time, meaning that the feedback mechanism is too slow to catch this sort of accident? OR! Is it that your body would rather risk pulling a muscle in your back than injuring the spine itself?



wrote …

I watched this just after coaching a group through 8 rounds of Tabata push-ups. Anyone who has witnessed Tabata PUs is familiar with what I call the "snake" where fatigue sets in and the athlete is unable to maintain the core stabilization and hips don't come up with the shoulders. But these are athletes who otherwise can hold a plank just fine. I wonder if this is a protection mechanism? If so, is it the reverse? Is the midline releasing in order to protect the shoulders?

thanks Coach, for a great video.


replied to comment from David Zink

I'm no expert on these elements, but I'd have to guess no. They are very different scenarios. In the snakey pushup, there is fatigue but not protection. The snaking changes both the load and angle of pressing. Holding the plank in that case makes the drill more difficult, not more dangerous. In the L-sit, if the hip flexors didn't release, you could theoretically damage the spine.

Speculating about Jared Van Anne's golgi feedback loop, it can't be that simple. There very well may be a feedback loop, but it's not just in a single joint. The midline begins to become unstable and the hip flexors release. I don't believe the golgi work systemically. Is this not the case?


wrote …

I windering if this phenomenon has something to do with the shoulders being independant (detoids) of eachother, whereas the legs via the L-sit are interdependant on the transverse abdominas, thereby too much load via both legs will result in too much load, thereby dropping the legs. However, when you raise the other shoulder up, it does not exert any extra pressure or load on the shoulder that's already raised.
So maybe this is a simple issue of maximal load for the muscles in use, and not something neurological?
I'd be very interested in anyones thoughts on this. It wasn't entertained as a possibility in the video.

Great content Coach, & Tony!


wrote …

The main stress here is on the muscles of the hip flexors holding the legs up, which would suggest a weakness in the hip flexors not midline destabilization. It could also be a balance reflex along the same line as catching yourself when falling. The person raises both legs, the weight of both legs tilts their upper body forward, and the body releases their legs to catch or counterbalance the torso.

Everybody has seen a rounded back deadlift or squat. It occurs because of a deficit in the strength of the erector muscles of the back. The legs and hips are strong enough to lift the weight, but the erector muscles aren't so the back rounds and puts the load on the spine, not the muscles. If there was a failure mechanism the legs and hips shouldn't be able to push the back into a rounded position. They would fail as the back rounded not continue to push and risk injury to the spine.

Muscle injuries occur because of forced lengthening of the muscle injured. Meaning that force applied to the injured muscle was greater than the concentric or isometric contractions, happened to fast for eccentric contraction to be utilized to protect the muscle, or in extreme cases stretched beyond its range.

With the exception of some impact injuries, bone and joint injuries occur because the muscle is not able to do its job and protect the bone or joint by mitigating the forces acting upon them. Repetitive/exercise induced impact injuries(stress fractures, arm wrestler's fracture of forearm) are caused by poor mechanics and fatigue. If the muscles are not used properly or too fatigued to function properly then the bone and joint are going to have to absorb the impact stress.

The only failure mechanisms are a strength/fatigue(not strong enough or too fatigued) failure mechanism, the conscious mechanism of not continuing to push/pull when you feel the midline destabilizing failure mechanism, and the letting go failure mechanism seen in heavy deadlifts or front squats. The human body was never designed to lift loads on the back. The load was meant to be lifted in the front while being supported by the arms. Not saying that you should neglect exercises like backsquats just think about that when using them that they are not part of natural human load lifting movement.

I know this was supposed to be about the L-sit not the backsquat, but if there was a failure mechanism it would be seen in that exercise more than any other because of the inherent nature of a poorly done backsquat to destabilize the midline and cause injury.

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